JPEG XL vs. Other Image Formats: Compression and Quality

There is no single image format that always delivers the smallest file at the same visual quality. JPEG XL (JXL) has useful strengths in lossless coding, progressive delivery and reversible recompression of existing JPEGs. AVIF can be smaller for some web-quality photographs, while the result for any format depends on the image, encoder, settings and quality target. Compare representative files at matched visual quality, then factor in encoding speed, features and the browsers your audience uses.

What JPEG XL is—and what it is not

JPEG XL is an image coding system standardized as ISO/IEC 18181. It supports lossy and lossless encoding, as well as lossless recompression of existing JPEG images. Its feature set also includes progressive coding, HDR and wide-gamut imagery, transparency, animation, layers, thumbnails and metadata. The JPEG Committee’s JPEG XL overview describes the reference implementation as free, open source and royalty free.

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That makes JXL broader than a like-for-like replacement for JPEG. Its capabilities may matter as much as its file size: a workflow that needs lossless preservation, progressive display or HDR support has different priorities from one that only needs a compact photograph for a web page.

The JPEG Committee gives a typical compression ratio of “20:1 to 50:1” in its overview. This is not a controlled comparison with AVIF, WebP or JPEG, and it is not a guaranteed ratio for a particular image. Treat it as a general description, not a prediction for your files.

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How JPEG XL compares with AVIF, WebP and JPEG

Different formats win in different tasks. The figures below are specific examples from Jake Archibald’s August 24, 2026 Mozilla Hacks article, not results that can be generalized to every photograph, screenshot or graphic. The lossy examples use the same SSIMULACRA 2 score within each row; the metric score is useful for that comparison, but matching a score does not make every image look identical to every viewer.

These examples show why a universal “smallest format” ranking is misleading: AVIF is smaller in the two cited lossy cases, while JPEG XL is smaller in the cited lossless cases. Mozilla’s discussion says JPEG XL is particularly useful for lossless imagery, progressive rendering and further compressing JPEGs without quality loss; it highlights AVIF for web-quality photographs and images that combine sharp edges with flat areas. Those are use-case pointers, not guarantees for every encoder or asset. See Mozilla Hacks’ JPEG XL article for its examples and context.

A separate AVIF comparison project, updated December 14, 2022, reports results that vary across quality, speed and lossless tests. Its listed decode timings used Chrome 110 development builds. Because the project is historical and its test conditions are specific, use it to understand how rankings can change with methodology—not as a current universal verdict.

Which format should you choose?

Choose JPEG XL when its capabilities or lossless behavior fit the job

• Lossless workflows: JXL was smaller than AVIF and lossless WebP in the cited fox example, and smaller than both in the cited dashboard screenshot example. Measure your own assets before expecting the same outcome.
• Existing JPEG archives: JPEG XL supports lossless recompression of JPEGs, so the image can be stored more compactly and later recovered without quality loss.
• Progressive delivery: Progressive coding can make an image render in stages as it downloads. Check the behavior of the browser and delivery path you intend to use; Safari does not support progressive download of JPEG XL files according to MDN’s format guide.
• Special image requirements: HDR, wide gamut, high bit depth, alpha transparency, animation, layers, thumbnails and metadata may affect format choice independently of file size.

Consider AVIF for web delivery, but validate your own images

AVIF may produce smaller files for some photographic images at a given visual-quality target. Mozilla’s selected lossy examples also show smaller AVIF files for both the fox photograph and dashboard screenshot, but those outcomes do not prove AVIF will win on your full asset library. Test the particular photographs, UI captures and mixed-content graphics you publish.

Keep WebP, JPEG or PNG when support or workflow calls for them

WebP, JPEG and PNG remain practical alternatives when they better fit the required browser or application support, image characteristics or existing pipeline. MDN recommends considering compression, image quality, breadth and depth of support, transparency and animation when selecting a format. JPEG XL does not make these factors disappear; a format supported by fewer of your audience’s clients may require a fallback.

How to run a useful compression and quality comparison

1. Build a representative test set. Include real photographs, screenshots, line art or logos, images with transparency, and mixed images with sharp edges and flat regions if those occur in your product. Use full-resolution source files, including high-density assets where relevant.
2. Encode each image with the settings you could actually deploy. Record the encoder and version, settings, color handling and whether the result is lossy or lossless. Quality-slider numbers from different encoders are not directly comparable.
3. Compare at matched visual quality. Adjust each encoder until results are acceptably similar for your use case. A perceptual metric can help organize comparisons, but inspect images visually too—especially text, edges, gradients, skin tones and fine texture.
4. Record more than output bytes. For each image and setting, capture file size, encode time and decode time on hardware relevant to your service and audience. Check visual artifacts and whether required metadata, color, alpha or animation behavior is preserved.
5. Test delivery in the intended clients. Verify decoding and rendering in the browsers and apps your users actually use, including fallback behavior. A compact file is not useful if a target client cannot display it.
6. Choose by workload, not a single winner. You might use one format for lossless archival and another for lossy web delivery. Keep the test inputs and results so encoder upgrades or changes to your audience’s support can be evaluated consistently.

The AVIF comparison project provides source test sets and methodology, though it was last updated in 2022. Mozilla’s advice is to test a representative image set at a quality that works for users and to optimize for high-density displays; its article phrases this as: “The key is to test with a representative set of images for your site, at a quality that works best for your users, and remember to optimise for high density.”

Browser support and fallbacks for JPEG XL

Browser support is a deployment constraint, not a permanent property of the format. MDN says JPEG XL support is not universal and recommends offering a fallback such as AVIF, WebP or JPEG through the <picture> element. Its guide lists Safari 17 and later, Chrome 145 and later behind the #enable-jxl-image-format flag, and Firefox preview releases; it also notes Safari does not support progressive download of JXL. These entries are version-sensitive: verify the current stable browser versions and actual audience support before relying on them. Mozilla’s August 2026 post describes Firefox and Chrome as intending to ship support, which is not confirmation that a final stable release has shipped. Can I Use’s live compatibility table can also change over time: check its current JPEG XL entries.

A <picture> element lets a browser select a supported source and then fall through to an ordinary image fallback:

<picture>
  <source type="image/jxl" srcset="/images/photo.jxl">
  <source type="image/avif" srcset="/images/photo.avif">
  <source type="image/webp" srcset="/images/photo.webp">
  <img src="/images/photo.jpg" alt="Description of the photograph">
</picture>

Confirm that the files exist, are served with appropriate image media types, and preserve the intended dimensions and accessibility text. Keep an appropriate JPEG or PNG fallback for clients that cannot use the newer sources; choose the fallback according to whether photographic compression or lossless graphics matter more.

Standards and implementation notes

JPEG XL is ISO/IEC 18181. ISO’s 2026 entry for ISO/IEC 18181-2:2026 identifies the third edition of Part 2, which specifies transport and container formats for metadata and extensions to JPEG XL codestreams. ISO says the edition technically revises the 2024 edition and adds an HDR gain map box. This matters for implementations that depend on container or metadata features; it does not change the need to check support in the specific software handling those files.

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For capturing website screenshots

If the task is to capture a web page as an image rather than choose a codec for existing image assets, try ScreenshotNeo as the screenshot API alternative. It returns a screenshot as PNG, JPEG or WebP, or a PDF; it is not an image codec and does not replace a JPEG XL encoder. Its clean-shot workflow handles cookie and consent banners, newsletter popups and chat widgets before capture. Sign up for 1,000 screenshots a month free, with no card required.

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